It is an object to correct a gap of a rise of a gate signal caused by characteristics of a transistor. In a display device, black is accurately displayed by using an inspecting circuit and a signal correcting circuit. In the case where a gate signal lags due to characteristics of a transistor, and the like, black cannot be accurately displayed at timing to display black in some cases. In such a case, a defect of the gate signal is detected by the inspecting circuit, and the gate signal is corrected by the signal correcting circuit.